Patent Document 1 discloses a naked eye stereoscopic vision display device. As shown in FIG. 1A of Patent Document 1, the display device comprises a light guide plate 2, light sources 1a and 1b which are so arranged as to be opposed to light incident surfaces of the light guide plate 2 on its both sides, a double-sided prism sheet 3 which is so arranged as to be opposed to the side of a light exit surface of the light guide plate 2 and has a light incident surface provided with a triangular prism row extending in a direction parallel to the light incident surface of the light guide plate 2 and a light exit surface opposite to the side of the light guide plate 2, which is provided with a semicylindrical lens row extending in parallel with the triangular prism row, a transmission type display panel 4 which is so arranged as to be opposed to the side of the light exit surface of the double-sided prism sheet 3, and a synchronous drive means 5 for driving the light sources 1a and 1b to light in synchronization with left and right parallax images which are alternately displayed on the transmission type display panel 4 and outputting light rays from the light sources 1a and 1b from the transmission type display panel 4 at angles corresponding to left and right parallaxes, respectively.
The display device has the effect of displaying high quality stereoscopic images with less crosstalk and allowing different images to be displayed simultaneously on the same screen since the light rays from the light sources 1a and 1b are emitted from the transmission type display panel 4 at angles corresponding to the left and right parallaxes, respectively.
Patent Document 2 discloses a backlight device using a reflection polarizing plate to emit linearly polarized light in order to achieve higher luminance of liquid crystal displays. As shown in FIG. 1 of Patent Document 2, the backlight device comprises a light guide plate 101b, a reflection polarizing plate 102 which is so arranged as to be opposed to the side of a light exit surface of the light guide plate 101b, a quarter wave phase difference plate 104 which is so arranged as to be opposed to a surface of the light guide plate 101b on the side opposite to the light exit surface thereof, and a reflection plate 103 provided on the side of a back surface of the phase difference plate 104.
In the backlight device, linearly polarized light out of exit light from the light exit surface of the light guide plate 101b which goes along a transmission axis of the reflection polarizing plate 102 passes through the reflection polarizing plate 102. On the other hand, the remaining polarized light is reflected by the reflection polarizing plate 102 and further reflected by the reflection plate 103, passing through the phase difference plate 104 twice, whereby the remaining polarized light is converted into linearly polarized light along the transmission axis of the reflection polarizing plate 102 and passes through the reflection polarizing plate 102. Thus, the polarized light out of the exit light from the light guide plate 101b which does not go along the transmission axis of the reflection polarizing plate 102 is multiply reflected between the reflection polarizing plate 102 and the reflection plate 103 through the phase difference plate 104, whereby the polarized light is converted into the linearly polarized light along the transmission axis of the reflection polarizing plate 102 and passes through the reflection polarizing plate 102. This increases the light use efficiency.
Since light is multiply reflected between the reflection polarizing plate 102 and the reflection plate 103 in this backlight device as discussed above, however, if this backlight device is used as a backlight unit of the naked eye stereoscopic vision display device of Patent Document 1, the backlight device arises a problem of crosstalk occurring between the left and right parallax images and this makes it difficult to display stereoscopic images.
Further, since the reflection polarizing plate is expensive, the manufacturing cost disadvantageously increases.
Patent Document 3 also discloses a backlight device like that of Patent Document 2.
Patent Documents 4 and 5 each disclose a backlight device in which a diffraction grating which scatters light with high directivity is formed on a light guide plate. Since light is reflected by using diffraction phenomenon caused by the diffraction grating, however, the backlight device has a problem that the direction of the diffraction varies depending on the wavelengths and there occurs color breakup due to the difference of the wavelength. Patent Documents 4 and 5 each have no mention about the polarization state of the exit light from the light guide plate and it is not certain if much polarized light to be effectively used for liquid crystal panels can be taken.
[Patent Document 1] WO2004/027492
[Patent Document 2] Japanese Patent Application Laid Open Gazette No. 11-64791
[Patent Document 3] Japanese Patent Application Laid Open Gazette No. 2006-236804
[Patent Document 4] Japanese Patent Application Laid Open Gazette No. 2004-319251
[Patent Document 5] Japanese Patent Application Laid Open Gazette No. 2004-319252